The objectives of this study will be to identify latent electrical activity within the recorded surface ECG originating from activation of atrial muscle, ventricular muscle, or specialized conduction tissue in normal and pathological conditons in the experimental animal and man. Our long term aims are to devise a Noninvasive technique for evaluating electrical activity not presently detectable in the surface ECG for diagnostic use in man. Such a technique would allow detection of lesions and impairment of function of the specialized conduction system as well as changes in myocardial activation in various pathological states, for example, ischemia and myocardial infarction. Our methodology is based on the analytical tool of signal averaging. This technique allows the extraction of a periodic signal contaminated with high levels of noise. Signal averaging has been used in physiologic and medical application such as fetal ECG and evoked response systems. Essentially, the procedure of signal averaging periodically adds, averages and stores information. Assuming that a signal is contaminated with Gaussian noise, whose mean value is zero, after many periods the result will be the desired waveform without noise. Thus this method can be utilized to detect a periodic waveform that is masked in noise.